The present invention relates to the art of diagnostic imaging. It finds application in conjunction with magnetic resonance imaging and will be described with particular reference thereto. However, it is to be appreciated that the invention may find further application in conjunction with other diagnostic imaging modalities such as computed x-ray tomography, positron emission tomography, ultrasound, digital x-ray, SPECT, and the like.
In medical diagnostic imaging, electronic image representations are generated and displayed as black and white images on a video monitor. Each pixel of the image has a gray scale which corresponds to a selected physical property of an examined object, such as tissue density, radiation absorption, and the like. Commonly, the displayed image represents a planar slice through the patient and the gray scale is selected to provide an image analogous to the appearance of such a slice if it could be physically taken. That is, the image has a readily apparent real life basis which simplifies understanding it.
The data used to generate the gray scale, anatomical image normally contains additional information which can be displayed directly or processed to derive further parameters corresponding to each of the displayed pixels. For example, a series of image representations of the heart can be collected each displaced in time. By displaying the images in sequence, a picture of the beating heart analogous to a moving picture can be created. The blood pumped by the heart has a gray scale which is not necessarily correlated to its velocity or direction of flow. In magnetic resonance imaging, the flow velocity of the blood moving through the heart can be determined with conventional algorithms. Traditionally, the flow velocity of the blood has been displayed by superimposing color on the black and white anatomical image. Each pixel was color coded in accordance with the flow direction, e.g. red for one direction and blue for the other. The intensity of the selected color was varied in accordance with the magnitude of the flow velocity. Analogously, other fundamental or derived parameters could be displayed by color coding.
One of the problems with the color coding technique is that it requires training to interpret. For example, blood or other flow rates in real life do not appear as different colors and color intensities. Rather, a radiologist must learn to translate the unnatural color variations into usable blood flow rate information.
Another problem with color coding is that it tends to overload the human visual channel. That is, in most imaging modalities there is so much information that could be displayed, video images cannot be color or otherwise coded sufficiently to convey all the information visually.
The color encoded video images not only required training to read, but also had limitations on accuracy. The human eye can only discern about 24 levels of gray scale and about 128 color hues. By contrast, the human ear can distinguish about 325 intensity levels and about 1800 frequency or pitch levels. Although the data was processed with a high degree of resolution or accuracy, the accuracy conveyed visually to the human observer was limited by limitations in the observer's powers of visual observation.
The present invention contemplates a new and improved imaging technique in which at least part of the available information is audio coded.